Pulse Sharpening with Metal-Oxide Bulk Switching Devices

Abstract : Certain niobium oxide (NbOx, x 2) materials are near insulating at room temperature fut undergo an insulator-to- metal transition near 800 deg C. A similar transition can be initiated at room temperature by applying an electric field. exceeding the threshold value, which depends on the oxygen concentration (x) of the NbOx. Metal-oxide threshold switch (MOTS) prototypes are obtained by applying appropriate contacts and packaging. Threshold voltages range from 100 V to several kV. A typical MOTS has a surge current capability exceeding 100 A, an off-state capacitance of only a few pF, and a switch delay of less than 0.5 ns. The latter two characteristics make the MOTS potentially superior to conventional devices for a number of high-speed, high-current switching functions. In particular, insertion of a MOTS into the output circuit of a conventional pulse generator can sharpen the leading edge of the pulse to yield a ns or even sub-ns risetime.